Since before recorded history man has attempted to decorate fabric with color. Starting with hides, and later woven and knitted materials, the traditional approach has been to liquefy the color by suspending it in a solution of water or some other fluid. The object to be dyed is then submersed in the solution or coated with it to produce the desired color.
Great skill was required to produce the desired color using this classic vat dyeing method, and even with today's sophisticated equipment great skill is still required to produce “dye lots” of the same color. Producing an exact color match is a product of recreating the exact intersection of color concentration, energy (usually heat) object material and processing time over and over in a chamber with constantly changing dynamics.
Skilled craftsmen all over the world dye hundreds of thousands of tons of fabric. As new sources of fiber (mostly polymer based) are developed, vat dying has become more difficult and problematic, among other things causing considerable water pollution. The net effect is unreliability in matching colors, and increase in energy use and dangerous effluents.
One solution is to use sublimation technology. In that process special dyes are printed onto a donor, the paper is juxtaposed against the receiver, and heat is applied to the outside surface of the paper. The heat causes the dyes to explode into a dye-laden superheated air colorant, and drives the colorant into the receiver. This use of superheated air as the carrying agent dramatically reduces both energy usage and pollution.
Although sublimation technology has been used for decades to produce relatively small, and usually complex images, it has never been used commercially in place of dyeing to cover relatively large areas of a receiver. The reason is that images are often recorded on the donor with defect lines. Such lines are rather irrelevant for small, complex images, because the area of deposition of any one visually distinct portion of the image is relatively small. But defect lines can produce very noticeable defects in printing of solids and relatively large, regular patterns.
Sublimation printing has also been commercially infeasible for double sided printing because of color differences on the two sides. Even if the dyes are identical on both sides of the receiver, the second application of dye tends to push the first application out of the paper and onto a take up paper, thereby producing visually different color densities. See e.g. US 2003/0217685 to Mason et al. (pub. Nov. 27, 2003), and US 2003/0035675 to Emery at al. (pub. Feb. 20, 2003). These and all other publications referred to herein are incorporated by reference in their entirety.
Still another disadvantage of sublimation printing is that it is entirely additive. Thus, if one prints a full color image on a yellow background, one must print over top of the yellow background, which distorts the colors of the image. Where multiple images or multiple passes are used, there can are also significant registering problems. See e.g., U.S. Pat. No. 6,393,988 to Gaskin (May 28, 2002).
All of these problems are exacerbated when manufacturing material with printing on both sides. Even where the fabric is sufficiently thick to prevent images from showing through from one side to another, inks and other colorants tend to interfere with color clarity due to bleed through. The current technology sews or uses a temperature sensitive adhesive to bind together two separately printed fabrics (for example with banners), and may also interpose an interliner or other intermediate stiffening sheet (for example with shirt collars). But such solutions are relatively expensive, and can result in an undesirable pillowing effect.
What is needed are methods and apparatus that employ sublimation techniques to print solids and other large blocks on both sides of fabrics and other receivers, with good color consistency and vastly improved consistent color saturation. It would also be desirable to apply such methods to legacy equipment. In particular, there is a need to permanently dye fabric using non-aqueous coloration process on a conventional heat transfer device, which preferably achieves exact or near exact color matching.